1. Tim Green, MGTS Precision Op Amp Applications Manager January 10, 2018
OPA2544 Bridge Circuit
Tim Green, MGTS
Precision Op Amp Applications Manager
January 10, 2018

2. Summary A) Power op amp circuits have several design considerations:
Thermal Design (heatsink, etc.)
Power Dissipation
Electrical Overstress from real world loads
Stability when driving cap loads
Small signal BW and slew rate limited large signal BW
B) OPA2544 Bridge circuit is analyzed to drive 10uF to 100uF cap loads and be stable. Large signal slew rate limitations must be considered when trying to drive the load at frequency. Slew rate across the bridge tied load is doubled from the slew rate out of either op amp. If slewing fast into cap loads current requirements must be analyzed. For each op amp output: Slew Rate = 2*pi*f*Vout_peak.
C) For more detailed design help use the resources sighted at the end of this presentation.
D) This presentation focuses on stabilizing the op amps to drive 10uF to 100uF load. The resulting closed loop small signal BW = 1.4kHz.
E) To minimize power dissipation use supplies as low as possible to yield maximum desired output swing.
F) Final PCB built design should confirm stability by a closed loop, small signal, transient stability test.
Note: All TINA-TI simulations can be run on the embedded schematics in this presentation by downloading the free TI SPICE simulator, TINA-TI, at:

3. Final Circuit

4. OPA2544 Bridge Circuit Stability Analysis

5. Master Loop – No Comp

6. Master Loop – No Comp, Modify 1/Beta for Stability

7. Master Loop – Final Comp
Since Master and Slave Op Amp are symmetrical relative to cap load, we will compensate Slave the same as Master and check for loop gain stability on each.

8. Master Loop – Final Comp
Loop Gain Phase Margin (10uF) = 123 degrees
Loop Gain Phase Margin (100uF) = 176 degrees

9. Slave Loop – Final Comp
Since Master and Slave Op Amp are symmetrical relative to cap load, we will compensate Slave the same as Master and check for loop gain stability on each.

10. Slave Loop – Final Comp Loop Gain Phase Margin (10uF) = 124 degrees

11. Closed Loop BW

12. Closed Loop BW

13. Key Design Resources
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